(a) Field of the Invention
The present invention relates to a method and apparatus for estimating a channel. More particularly, the present invention relates to a method and apparatus for selecting encoding and modulation methods by estimating a channel based on weather data in a satellite broadcasting communication system.
(b) Description of the Related Art
A Digital Video Broadcasting Second Generation (DVB-S2) method, which is a standard of a European type of satellite broadcasting communication method, uses an adaptive coding modulation (ACM) technique in order to improve transmission efficiency further by 30% or more than an existing DVB-S method. The ACM technique is a method of coping with a satellite channel characteristic in which link quality changes and provides high band efficiency and throughput by optimally selecting encoding and modulation methods for a channel state according to a signal attenuation degree on a satellite link.
According to the ACM technique, a terminal measures a channel state and automatically selects appropriate encoding and modulation methods based on a measurement result. Alternatively, in order for a central station to enable selection of appropriate encoding and modulation methods, the terminal transmits a present signal-to-noise ratio (SNR) value to a central station through a backward link. Thereafter, the central station changes the encoding and modulation methods to those that are requested by the terminal using received information, or estimates and determines the most appropriate encoding and modulation methods based on an SNR value that is transmitted by the terminal and encodes, modulates, and transmits data of a forward link according to the determined encoding and modulation methods.
When the terminal transmits measured information (e.g., an SNR value and information that requests selection of encoding and modulation methods) to the central station through a backward link, the terminal transmits the information using a user diagram protocol (UDP) format. In this case, when a geostationary orbit satellite is used, due to a long transmission delay time (e.g., about 250 s), which is a characteristic of a satellite network, an SNR value that is used when the central station determines encoding and modulation methods already becomes outdated data.
Moreover, when an ACM control message from the terminal is transmitted using a UDP protocol having no reliability, a corresponding packet may be damaged. In this case, because a time internal between measurement data sample values, which are SNR values that are transmitted from the terminal for ACM selection, further increases, an accurate state of a present forward link may not be known and a more outdated value is used as a sample value. Therefore, a method of selecting encoding and modulation methods by more accurately estimating a channel state in which data is transmitted is requested.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.